1. Field of the Invention
The present invention relates to a method and apparatus for inspecting defects on a polishing pad to be used with a polishing apparatus for performing chemical mechanical polishing of a wafer.
2. Description of the Prior Art
In a semiconductor manufacturing process, surfaces of wafers coated with predetermined thin films may not be frequently flat. If surfaces are not uniformly even, an accurate circuit pattern cannot be obtained from the next photolithographic process. In order to avoid such a problem, the surface which is not flat should be polished. That is, the wafer is spun or rotated in a state where it is pushed toward a polishing pad while spraying slurry, i.e. a suspension which includes inorganic particles and surfactants, onto the polishing pad. Then, the wafer surface can be polished to be flat through the combination of mechanical friction between the wafer and suspension and chemical dissolution reaction of the suspension. This process is called chemical mechanical polishing (CMP).
Recently, since a critical dimension of the semiconductor has rapidly decreased, a process tolerance which is permitted in the photolithographic process has also rapidly reduced. Thus, the need for chemical mechanical polishing has remarkably increased. Most domestic and foreign semiconductor factories have introduced several dozens of the polishing apparatus per factory while introducing this process.
One of the problems of the process is that a surface scratch occurs during the polishing process. In a case where a surface of the wafer is severely scratched, the wafer may be discarded due to potential damage to a circuit to be printed on the wafer. That's because even a fine scratch will deteriorate efficiency of the next photolithographic process, thereby reducing throughput yield.
There are several reasons why such scratches are generated. First, a scratch may result when excessively large inorganic particles are included in the slurry. Further, the scratch may be produced when the particles in the slurry are agglomerated during the polishing process. Furthermore, the scratch may be produced when any external particles are dropped onto the pad. For example, any metallic fragments may drop from mechanical parts of the polishing apparatus. In addition, diamond particles produced during diamond pad conditioning, performed to improve an operating condition of the pad used for a specific period of time, may cause a scratch. Moreover, if any particles are dropped on the polishing pad before the polishing operation or any particles included in the polishing pad protrude from a surface of the pad when the pad intends to be used, problems are caused.
The problems occurring from the slurry have been greatly solved by inspecting the slurry using various measuring equipment and by filtering out unnecessary particles using some filters. The problems resulting from a diamond pad conditioner have also been almost solved through endeavors to improve quality of the conventional diamond pad conditioner. However, sufficient methods for the inspection or processing of the defects on the polishing pad itself have not yet been achieved.